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carbohydrate-binding module Fa from Bacteroides thetaiotaomicron SusE, and similar CBMs. CBM-Fa is the first of three starch-specific CBM (carbohydrate-binding modules) of SusF, a cell surface lipoproteins within the Sus (Starch-utilization system) system of the human gut symbiont Bacteroides thetaiotaomicron. The precise mechanistic role of SusF in starch metabolism is unclear. SusF has an N-terminal domain which may belong to the immunoglobulin superfamily (IgSF), followed by three tandem starch-binding CBMs: CBM-Fa, -Fb, and -Fc; F denotes SusF, and they are labeled alphabetically from the N- to C- terminus. These CBMs have no enzymatic activity. Each starch-binding site contains an arc of aromatic amino acids for hydrophobic stacking with glucose, and hydrogen-bonding acceptors and donors for interacting with the O-2 and O-3 of glucose. These three CBMs show differences in their affinity for various different starch oligosaccharides, and they contribute differently to binding insoluble starch. CBM-Fa does not bind insoluble starch, and can bind smaller maltooligosaccharides. Proteins in this subgroup are present in the species of the Gram-negative Bacteroidetes phylum. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",